Antigen-specific antibodies increase the uptake of antigen, resulting in enhanced T cell activation (Chang, T. W., Immunol. Today, 6:245, 1985). Antibody:antigen immune complexes bind to Fc receptors present on the surface of antigen presenting cells (APC), such as macrophages. These complexes are then internalized and the antigen is processed and presented in the context of MHC-encoded molecules to antigen-specific T cells. Thus, the presence of antigen-specific antibodies can reduce the level of antigen required to activate T cells (Gosselin, E. J., et al., J. Immunol., 149:3477, 1992).
Receptors for the Fc portion of IgG (Fcxcex3R) have been characterized at the molecular level. Human monocytes and macrophages express three major classes of Fcxcex3R, identified as Fcxcex3RI, Fcxcex3RII, and Fcxcex3RIII. Targeting tetanus toxoid to either Fcxcex3RI or Fcxcex3RII on monocytes reduces the concentration of antigen required to stimulate T cell proliferation in vitro by a factor of 100-1000 (Kovacsovics-Bakowski, M., et al., Proc. Natl. Acad. Sci. USA, 90:4942, 1993). Therefore, targeting antigen to specific Fcxcex3R on APC can dramatically decrease the amount of antigen required to stimulate a specific T cell response.
Following phagocytosis by a monocyte or a macrophage, antigens can be processed and presented to cytolytic T lymphocytes (CTL; Falo, L. D., et al., Nat. Med. 1:649, 1995). It has been shown that mice immunized with an iron particle coupled to a tumor antigen are protected from tumors expressing that tumor antigen (Kovacsovic-Bankowski, M., et al., ibid). Therefore, by inducing monocytes or macrophages to phagocytose tumor antigens, protective immunity to tumors can be induced.
The present invention provides a cell which is transformed to express on its surface a component which binds to an Fc receptor of an effector cell. In particular embodiments, the Fc receptor binding component on the cell is an antibody or portion thereof, such as a single chain Fv fragment, which binds to the Fcxcex1 receptor or the Fcxcex3 receptor present on effector cells. The transformed cell is thus targeted to the effector cell via the Fc binding component, and can be used as a vehicle to increase an effector cell-mediated immune response, such as cell lysis and phagocytosis, against an antigen associated with the cell. Examples of target antigens include, but are not limited to tumor antigens, such as HER-2 neu, TAG 72, carcinoembryonic antigen and gastrin releasing peptide receptor, and components from pathogens, such as a virus, fungus, protozoan, or bacterium.
The anti-Fc receptor binding component is produced recombinantly within the target cell in a manner which causes it to be expressed on the surface of the cell. In a preferred embodiment, the anti-Fc receptor binding component is able to bind an Fc receptor of an effector cell without being blocked by endogenous antibody, e.g., IgG or IgA. In another preferred embodiment, the anti-Fc receptor binding component is an antibody or antibody fragment, such as an IgA, IgG, IgM, IgE, or fragment thereof (e.g., Fab, Fabxe2x80x2, F(abxe2x80x2)2, Fv, or single chain Fv fragment).
In a particular embodiment of the invention, the anti-Fc receptor binding component is expressed recombinantly as a fusion protein associated with the membrane of the target (transformed) cell. For example, the anti-Fc receptor binding component can be expressed in the cell as a fusion protein together with a transmembrane protein or portion thereof (e.g., transmembrane domain of the protein). In such embodiments, a preferred anti-Fc receptor binding component comprises an anti-Fc receptor antibody or antibody fragment, such as humanized anti-Fcxcex3R antibody 22 (H22) having the ATCC deposit number CRL 11177, anti-Fcxcex1R monoclonal antibody A77 (Monteiro et al. (1992) J. Immunol. 148:1764).or a single chain Fv fragment of H22 or A77. In a particularly preferred embodiment, the anti-Fc receptor binding component is expressed as a fusion protein made up of a single chain Fv fragment of H22 or A77 and a transmembrane protein (e.g., the transmembrane domain of the platelet derived growth factor receptor).
Accordingly, in addition to cells that express Fc receptor binding components, the present invention also provides vectors and expression plasmids, such as anti-Fcxcex3R pJG717 (SEQ ID NO:1) and anti-Fcxcex1R pJG718 (SEQ ID NO:3), which can be used to transform cells so that they express components which bind Fc receptors.
The present invention further provides a method of increasing an immune response in a subject using transformed cells of the invention. The method involves contacting the transformed cell with an effector cell in the presence of a lymphocyte, (e.g., a T cell or B cell). In one embodiment, the effector cell is treated with an agent that increases expression of Fc receptors on the surface of the effector cell. Suitable agents include cytokines, such as granulocyte-colony stimulating factor (G-CSF), granulocyte-macrophage-colony stimulating factor (GM-CSF), xcex3-interferon (IFN-xcex3), tissue necrosis factor (TNF), and combinations thereof.
Cells of the present invention can be transformed to express Fc receptor binding components either in vivo or ex vivo. In a preferred embodiment, the cell is transformed ex vivo and is then administered to a subject in vivo. Following administration, the cell binds to an effector cell via an Fc receptor of the effector cell (e.g., Fcxcex3 receptor, an Fcxcex1 receptor, an Fc xcexc receptor, or Fcxcex5 receptor). In particular embodiments, the Fc receptor is an Fcxcex3 receptor selected from Fcxcex3RI, Fcxcex3RII, and Fcxcex3RIII. Alternatively, effector cells can be taken from the subject by, for example, apherisis, modified with cytokines to optimize antigen presentation and Fc receptor functions ex vivo, combined with cells of the present invention transformed to express Fc receptor binding components, and then returned to the subject.
Among various other uses, transformed cells of the present invention can be used to induce a specific immune response against an antigen associated with the transformed cell, such as a T lymphocyte mediated immune reponse. Accordingly, transformed cells of the invention can be used to achieve protective immunity against selected antigens, e.g., as vaccines. When targeting tumor cells, for example, the present invention provides the distinct advantage in that no particular tumor antigen need be known or selected for targeting. This is because the entire tumor cell itself is transformed to express a component which binds to an effector cell via an Fc receptor to cause killing of the tumor cell. This is of great benefit since many tumors do not have defined antigens for targeting.